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Author Topic: Ordered an sdr-iq...  (Read 71102 times)
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Mike/W8BAC
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« Reply #25 on: January 26, 2010, 02:20:16 PM »

Short of starting a new thread Tom, try this.

I purchased a 40 DB iso "T" years ago for tapping into repeater antenna circuits to inject weak signals or monitoring. It was expensive and I couldn't resist finding out how it worked.

It was an SO239 "T" with something odd. The long  portion was normal but the branch or "T" line didn't have the spring clips that contact the center pin of the PL259. I found out the manufacturer simply disassembled the T and ground off the clips and a small amount of the stud that threads into the long rod. I assumed they calibrated it to 40 DB of isolation and reassembled it.

Since than I have made 5 or 6 of them. I use one in my QRO line for the frequency counter and another for the HP spectrum analyzer. Either instrument would fry with high power on them.

With 40 DB of isolation I suspect an SDR receiver would be very safe. If you need more isolation just grind more off. Don't forget a small dab of lock tight to keep the stud from backing out.

Mike
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N2DTS
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« Reply #26 on: January 26, 2010, 02:46:39 PM »

I am going to try a small antenna, right on the radio, since I wont be using it as the regular receiver.
When I had one, I left it hooked up in the den, and ran a cable to the station control, and even with full power going through the station control box did not blow up the sdr-iq.
The sdr-iq was not selected, but there is a lot of rf in the station control box...

Yes, I built the amplifier, like usual using no known design, so need to test things and see just how dirty or clean it is, and where the high voltage and drive levels need to be for the cleanest output.

I really don't run the flex into the amplifier very often, as its only good for about 175 to 200 watts out in AM, but I still want to know what is up with the amp...

It will also be interesting to see what happens when I jam into the neg cycle loading setup on the 3x4D32 rig, or overmodulate on the 2X813 rig, and just how wide the 32v3 splatters....
I can record it with the sdr-iq and study it!

Someone here said something about neg cycle loading being nasty with a floating screen setup, and I would like to do some experiments with running the screen voltage at a fixed point and leaning into the ncl and see what happens.

Brett
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k4kyv
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Don
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« Reply #27 on: January 26, 2010, 04:53:45 PM »

Has anyone tried out the SDR-14, and compared it to the SDR-IQ?  Is the -14 actually worth 2X the -IQ, per the price?
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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« Reply #28 on: January 26, 2010, 04:57:41 PM »

The cleanest exciter I have ever seen is the HPSDR Penny at third order -55 dB  on 20 meters. I'm told it is even better on 75.
When I was testing the ERB amps I used a pair of HP8640B generators into a combiner to measure IMD. I was able to get into the mid 30s but never had the bias set high enough. Even the old HP audio generators had harmonic levels of -26 dBc so it makes it very hard to check an amp with high audio harmonic outputs. This is why I used RF sources throwing harmonics well out of the test frequency range. I bet a quality sound card could generate a clean two tone signal. so be careful with your source and make sure you can measuer it before you test an amplifier.
I think the problem in the EB104 is the transformer design. Also the shunt choke is too small. I would think MRI amps need to have low IMD.
FLEX is stuck in the past with a DDS source which has close in spurs. This helps to generate IMD. My homebrew Softrock is pretty clean since it has a crystal oscillator through a divider.  The softrock properly connected to a receiver will only be limited by the receiver and the sound card it is connect to.
The dynamic range of the softrock can be shifted up by reducing the gain of the two opamps after the tayloe mxer.
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Steve - WB3HUZ
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« Reply #29 on: January 26, 2010, 05:44:36 PM »

None of this is really relevant to measuring IMD using the appropriate two-tone input.
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N2DTS
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« Reply #30 on: January 26, 2010, 06:52:57 PM »

I don't know if the sdr-14 is a better receiver, maybe its a little better, but it does a 30Mc panadaptor display.
Not sure why anyone would want that, that is a lot to look at on one screen!

Brett
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K1JJ
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« Reply #31 on: January 26, 2010, 07:01:09 PM »

Yes, the two-tone test gives a standardized measurement that can be used across different rigs and situations.

Until I set up a good SDR spectrum analyzer with two-tone test, I will continue using a receiver.  A receiver is a great spectrum analyzer! Once I had a good idea of how my linear amplifier system was performing after Steve's spec analyzer visit, I then used my FT-102's receiver as relative guide to improvements. I used the nastiest sounding word I could find that generates crud up the band. Believe it or not, an exaggerated  "Yallo" does the trick. Normal talking doesn't come close... The Tron knew what he was doing back then....Grin

I put a 24" ant wire on the back of the FT-102 and rolled it up or pulled it out to give a standardized S9 +40 over with full power into the dummy load using the test transmitter.  Set the RX bandwidth to 2.8 khz LSB and tune UP the band (in LSB) while socking a Yallo into the TX on LSB ssb. After the normal audio bandwidth of 2.8khz, the audio will disappear and the crud level will start. I found a good signal should have less than S9 crud at 3.1khz away. I was able to get it down to less than S5 crud with some sweet spot adjustments like VERY heavy loading of the IPA, high final idle, heavy final loading, low output of the  driver, etc. These S meter levels are relative - yours will be different.  

Be sure the TX signal is not bypassing the antenna and getting into the RX - test this by disconecting the receiver antenna. There shud be little signal.   Once you get a feel for what a good signal should sound like using your clean barefoot exciter, then add the linear and see what it does. Be sure to renormalize the receiver to S9 +40 over by rolling up the antenna wire a little, etc. Your bandwidth results will vary based on the filters, etc, but learn what a clean signal sounds like and go from there.

Bottom line is until a good spec analyzer is available, a good receiver can do an excellent relative job for testing and improvements.

T
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« Reply #32 on: January 27, 2010, 08:10:41 AM »

I downloaded the new spectraview software, and also the new sdr console.
Spectraview has improved since I last used it, with various sliders on the screen to adjust things, rather than opening menu's to get to things.
They still don't have drag and drop passband shift, and filter widths, maybe in the future...

Sdr console has band buttons, but is still in development, and lacks a few things.
Both do not include sync AM yet.

Makes you want to be a geek and learn how to make your own program to control these things....
Flex is working on new software, who knows when its going to be done, and how many bugs its going to have in it, but it should make a great radio much better....
There is a LOT of very neat stuff they could do if they got their butts in gear.

All these efforts seem to be mostly one man operations, done by people in their spare time.
Makes you wonder why the Japanese don't jump in and blow the one man shows away, or even Ten Tec....

Brett


 
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W3RSW
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« Reply #33 on: January 27, 2010, 12:13:24 PM »

Following the topic points relative to my QS1R.  My T/R relay's rcvr. terminal is also grounded on transmit; easy transmit signal monitoring.  I like the idea of a two inch or so stub antenna for monitoring all the shack's rigs.

Quote
None of this is really relevant to measuring IMD using the appropriate two-tone input.

Steve, you should have been a technical writer...  relevant, succint and to the point.  Grin
.. or are you?
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RICK  *W3RSW*
Steve - WB3HUZ
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« Reply #34 on: January 27, 2010, 12:19:31 PM »

I'm completely irrelevant. The point is, however, relevant.
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Carl WA1KPD
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« Reply #35 on: January 27, 2010, 01:31:18 PM »

Have had mine for about a year and I love it. I use it at home a lot and have found it very interesting to use compared to the regular panoramic display ion my Icom 756. I have found a lot of odd signals across the entire spectrum and see things I never hear- Some of the govt testing stuff I guess.
I use it in conjunction with "go to my pc" to log in on business trips and listen to what is going on back home. Depending on the speed of the local connection I sometimes have to back off the graphic intensive waterfall display.

Spent many nights listening to local 160 or 75 AM when cross country or out of country

Right now it si my favorite rcvr.

One thing of interest is that if I listen to the SDR-IQ and a regular rcvr there is a delay of maybe 1/2 a second in the audio from the SDR.

Carl

/KPD
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Carl

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k4kyv
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« Reply #36 on: January 27, 2010, 01:36:33 PM »

I have been entertaining the idea of purchasing the SDR-IQ, now that I have a laptop that I can easily transport to the shack, but would probably use it more as a pan adaptor and a piece of test equipment than as the main station receiver.

It would be interesting to compare its AM reception to that of the 75A-4/Sherwood combination, and its selectivity to that of mechanical filters.  Bernie, W8RPW says he prefers to run his off the i.f. of his 75A-2 or HRO-60, than to use it as a stand-alone receiver.

If I were surprised and it really did out-perform all my present receivers, I would probably still want to add a passive stage of selectivity, something like a scaled down version of a wide range antenna tuner built with receiver grade components, between it and the antenna.  My Kenwood R-1000 picks up an incredible amount of images, heterodynes and buzzies on the longwave band, but adding a simple tuned circuit to the  front end pulled the European longwave broadcast signals right out of the background noise, even to entertainment quality at times.  Most present day solid state receivers have little or no front-end selectivity other than a series of broad bandpass filters that cover up to an octave of spectrum each.  It is bound to hamper reception when the active first stages of the wide-open receiver front end are being bombarded and pounded with strong signals over a swath of several megacycles each side of the station you are trying to tune in.

I recall some years ago a ham friend about 8 miles away bought an expensive solid state transceiver of the era that was supposed to have an excellent receiver section, but he was perplexed by the persistent fact that I could comfortably receive stations on my pre-WW2 HRO equipped with outboard mechanical filters, that he couldn't even hear on his ricebox.  He wasn't using a shabby antenna, either.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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http://www.mwbrooks.com/dvorak
Steve - WB3HUZ
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« Reply #37 on: January 27, 2010, 02:18:04 PM »

I can't speak for the SDR IQ thingie, but well implemented digital filters will outperform any analog filter. Even current day crystal filters are superior to the revered Collins mechanical filters.
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WB2EMS
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« Reply #38 on: January 27, 2010, 02:22:05 PM »

K4KYV said
Quote
It would be interesting to compare its AM reception to that of the 75A-4/Sherwood combination, and its selectivity to that of mechanical filters.  Bernie, W8RPW says he prefers to run his off the i.f. of his 75A-2 or HRO-60, than to use it as a stand-alone receiver.

I suspect you're right that some front end preselection wouldn't hurt. And I also suspect that the phase noise would limit it's absolute performance compared to some receivers with analog VFO's. But good enough is the enemy of better and I find myself listening to it more and more because of it's convenience. I've been using it mostly remotely, even in the house as well as the office.  

Don, why don't you hit up sdr-radio.com and download the software and make a connection to my sdr-iq or some of the others around and give a listen compared to what you are hearing with your rigs. It won't be a direct comparison - different locations and antennas, but might shed some light on the issue. I'm not sure the sdr-radio software gets quite the performance out of the unit that the spectravue software does, but at least it's a start.

BTW - nice to chat with you the other night.
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73 de Kevin, WB2EMS
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« Reply #39 on: January 27, 2010, 03:31:13 PM »

I cant say if you would find better performance out of the sdr-iq, its more a low end product, but it did seem quite good in my shack. Not as quiet as the homebrew, but I had no overload issues, no problems with super strong broadcast band signals, etc.

Get one just for the spectrum display, for doing tests, monitor uses, and the panadaptor.

The flex 5000 DOES seem to be better then almost everything else out there that I have tried, its also not quite as quiet as the homebrew, but has sync detection, passband tuning, the ability to see and move the filter around with a mouse, you can have ssb qrm and slide the filter over (on one side) just till it clears the qrm, and its gone!

I suspect the sdr-iq software will get much better over time...

Brett
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« Reply #40 on: January 27, 2010, 03:42:33 PM »

Have had mine for about a year and I love it. I use it at home a lot and have found it very interesting to use compared to the regular panoramic display ion my Icom 756. I have found a lot of odd signals across the entire spectrum and see things I never hear- Some of the govt testing stuff I guess.
I use it in conjunction with "go to my pc" to log in on business trips and listen to what is going on back home. Depending on the speed of the local connection I sometimes have to back off the graphic intensive waterfall display.

Spent many nights listening to local 160 or 75 AM when cross country or out of country

Right now it si my favorite rcvr.

One thing of interest is that if I listen to the SDR-IQ and a regular rcvr there is a delay of maybe 1/2 a second in the audio from the SDR.

Carl

/KPD

Yes, Carl I have noticed the audio latency between the SDR-IQ and the transceiver.  I have to listen to one or the other.   But the delay is very noticeable in the SDR-IQ.  I don't know if this is a function of the receiver itself, or the software.  I don't know if there is any way to reduce the delay or not.

73,  Jack, W9GT

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73, Jack, W9GT
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« Reply #41 on: January 27, 2010, 04:08:37 PM »

Yes, Carl I have noticed the audio latency between the SDR-IQ and the transceiver.  I have to listen to one or the other.   But the delay is very noticeable in the SDR-IQ.  I don't know if this is a function of the receiver itself, or the software.  I don't know if there is any way to reduce the delay or not.

Unlikely.

There will always be latency when performing FFT filtering. This is because FFT filtering requires some number of samples to work. The sharper the filter, the longer the latency.

Analog filters have a similar effect, but their latency is small enough that it manifests itself as a phase shift.

Since digital filtering cannot be done on a per-sample basis, there will always be a delay until sufficient samples have been accumulated before there will be any output from the filter.

This is why I'm not big on the approach of digitizing the entire spectrum and using FFT to segregate the information you want from the information you don't. It's a tremendous waste of processing power, and doesn't address the issues that a selective RF section and IF filtering are intended to deal with (front-end overload and IMD, to name a few).

It will be some time before the technology is in place to allow flexible digital filtering with low latency, and zero latency in any digital system is physically impossible.

Even the bleeding-edge technology we use at work (a military SDR project) introduces a noticeable latency, with some of the best DSP talent in the field working on it. It's par for the course.

Still a darn handy tool for the shack, though.

--Thom
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« Reply #42 on: January 27, 2010, 04:29:32 PM »

Thanks Thom!  Well at least we know it is an "expected" phenomenon.  It can be annoying if you try to listen to both at once.  There's a little too much delay to call it an echo effect.  In practical use, however, if you turn off the audio from the SDR-IQ, you really don't notice the delay that much when looking at the spectrum display. 

As for the point about looking at the whole spectrum.  Isn't the SDR-IQ just looking at 190 KHz at a time?

73,  Jack, W9GT
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« Reply #43 on: January 27, 2010, 05:20:51 PM »

As for the point about looking at the whole spectrum.  Isn't the SDR-IQ just looking at 190 KHz at a time?

You are correct.

I wasn't actually referring to the SDR-IQ with that comment, but some SDR packages do take that approach. "Because we can" is often equated to "best practice" when it really shouldn't be. There are some things that can be done in software that are still better left to hardware at this point in our technological evolution.

With today's technology, my preference would be analog RF and 1st IF, with a digital 2nd IF and AF for a complete transceiver, but that's just me. Proof-of-performance applications (such as what's being discussed here) and other bench roles are a better application of "software everything", if you don't mind the added latency of additional FFTs in the signal path.

Every good thing has a down side. All in all, latency is the only guaranteed drawback to any DSP-based system. The reward is usually well worth the sacrifice.
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KF1Z
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Are FETs supposed to glow like that?


« Reply #44 on: January 27, 2010, 05:41:53 PM »

The only time the latency seems to be an issue, is while trying to monitor yourself..

Luckily with the QS1R the latency is so low, it gives the feeling of being in a large room....  (less than 50ms)  not quite an "echo".

That is, in part, because there is no soundcard in the system. (CAN be, but no need for it).

Still just enough to make it a little annoying.....

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KA1ZGC
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« Reply #45 on: January 27, 2010, 08:15:57 PM »

Luckily with the QS1R the latency is so low, it gives the feeling of being in a large room....  (less than 50ms)  not quite an "echo".

That is, in part, because there is no soundcard in the system. (CAN be, but no need for it).

BINGO. I didn't even think of that. There's ALWAYS buffering at the soundcard. The more buffers your audio has to bucket-brigade its way through, the longer the propagation delay is going to be, and the more buffer management the processor has to deal with (which really hurts if the same processor is also performing the DSP arithmetic).

Hardware definitely makes a difference.
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N2DTS
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« Reply #46 on: January 27, 2010, 08:25:17 PM »

The reason the latency is higher on the sdr-iq is because it uses the computer sound card.
The qs1r has its own built in d/a converter and latency is VERY low.
It costs $1000.00 though, and might be dropped if the designer decides to do something else, or gets a real job or something...
The persius uses the computer sound card, and latency is very high.
Its just behind the K3 as the 2nd  best receiver on the sherwood list.
Don's 75A4 is not on his list...


And the sdr-iq DOES sample and digitize the entire 500 Hz to 30 MHz, and sends the 190 KHz you want to the display.
At least, that is how I understood it.
Quote below....


The hardware samples the whole 0.0001-30 MHz band using a high performance, 14 bit analog to digital converter (ADC) running at 66.6 MHz.

What gets me is that the box is so small for all the stuff you can do with it, and on top of making a good piece of test equipment, its also a good receiver.
The interesting things you see, I had no idea what some of them were.

I think the display is better then the current flex software.
But things are only going to improve on this stuff as they work on the software.

I don't suppose it will be long before they have great radios, rx and tx using the direct digitizing like the sdr-iq, but much faster and cleaner.

Brett
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WA1GFZ
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« Reply #47 on: January 27, 2010, 08:28:36 PM »

A/D into DDC is a lot faster.
Tom,
The FT102 has a dynamic range of 85 db so S9 plus 30 is close to the level the rX starts generating internal IMD if the S meter is anything close to reality.
Any amplifier will generate IMD if you drive it hard enough.
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KF1Z
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Are FETs supposed to glow like that?


« Reply #48 on: January 27, 2010, 08:29:33 PM »

That's right Thom.

Actually, if I use the soundcard with the QS1R...
After a few minutes, you can see/hear the delay.

I mean to say if you're watching the display.... the sound lags behind the display..
By, oh, I'd guess as much as 500ms after a while.

If I stop the RX, and restart it, the ssoundcard buffer clears, and the display and sound will be just about in sync for a while... and the process repeats..

But I use the DAC that is on-board the QS1R for headphones and there is very little latency. (set for 50ms... can go a little lower).


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« Reply #49 on: January 27, 2010, 08:38:07 PM »

Designer of QSR1 has a job, You might want to check him out.... and he doesn't need a job.
Perseus is a similar design just one generation older and slower A/D. I think th esound card just drives a speaker.
Coming soon a 1/2 watt transceiver from HPSDR. This is the one to wait for. It will have the same performance as the HPSDR project but all on one 4 by 6 board.
The first two boards are in test.
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